Place the aubergine slices in a colander and sprinkle them with salt. Leave to drain for 20 minutes to remove excess liquid, then rinse well in cold water and pat dry with paper towels.

Meanwhile, place the oil and onions in a medium bowl and cook, covered, for 6 minutes. Set aside.

Place 250 gms of the aubergines in the base of a flameproof 2 litre casserole dish.

Spread the onions on the aubergines, and then spread the tomatoes over the onions. Sprinkle with salt and pepper and 1½ teaspoons of the basil.

Arrange the remaining aubergines on top and sprinkle over the remaining basil.

Cook, covered, for 15 minutes.

Sprinkle over the cheese and cook under a preheated conventional grill until the cheese topping is brown and bubbling.